The present invention relates to a magnetic recording medium used in, for example, peripheral devices of calculators, or magnetic disk apparatuses for recording of image and sound data; a process and apparatus for producing the magnetic recording medium; and a magnetic recording and reproducing apparatus incorporating the magnetic recording medium.
As recording density of magnetic recording media is increased, there have been proposed reduction in noise and enhancement of resolution by means of, for example, micronization or magnetic isolation of magnetic grains in a magnetic layer, or thinning of a magnetic layer.
However, when magnetic grains are micronized or magnetically isolated, or when a magnetic layer is thinned, the size of the magnetic grains is reduced, and therefore, thermal stability (i.e., thermal decay resistance) of the resultant magnetic recording medium tends to be deteriorated. The term xe2x80x9cthermal decayxe2x80x9d refers to a phenomenon in which recording bits become unstable and recorded data are lost. In a magnetic recording and reproducing apparatus, thermal decay is manifested in the form of reduction in reproduction output of recorded data with passage of time.
Hitherto, typical substrates for producing magnetic recording media are non-magnetic metallic substrates formed from, for example, an aluminum alloy. Usually, a hard film formed from NiP or similar material is provided on such a non-magnetic metallic substrate in order to harden its surface, then the surface of the substrate is subjected to texturing, and the substrate is used for producing a magnetic recording medium.
Texturing is a process for forming irregularities on the surface of a substrate along a predetermined direction (usually in a circumferential direction) of the substrate. When the surface of a substrate undergoes texturing, the crystal orientation of an undercoat layer and a magnetic layer, which are formed on the substrate, is enhanced, and the magnetic anisotropy of the magnetic layer is enhanced, and thus magnetic characteristics, such as thermal stability, of a magnetic recording medium can be enhanced.
In recent years, instead of a metallic substrate formed from aluminum or similar metal, a non-metallic substrate formed from material such as glass or ceramic has been widely used as a substrate for producing a magnetic recording medium. Such a non-metallic substrate has an advantage that head slap does not easily occur in the substrate, due to high hardness of the substrate. Furthermore, from the viewpoint of glide height characteristics, such a non-metallic substrate is advantageously used, because of its excellent surface smoothness.
However, a non-metallic substrate such as a glass substrate encounters difficulty in undergoing texturing, and involves problems that the magnetic anisotropy of a magnetic layer becomes unsatisfactory, and thermal stability is inclined to be deteriorated.
In order to solve such problems, there has been proposed formation of a hard film which can be easily textured on a non-metallic substrate formed from material such as glass or ceramic.
For example, Japanese Patent Application Laid-Open (kokai) No. 5-197941 discloses a magnetic recording medium including a non-metallic substrate coated, by sputtering, with a NiP film serving as a hard film which is easily textured.
A magnetic recording medium including a hard film formed on a non-metallic substrate is produced by the following process: the hard film is formed on the substrate in a film formation apparatus such as a sputtering apparatus; the substrate is temporarily removed from the apparatus and subjected to texturing by use of a texturing apparatus; the resultant substrate is again placed in the film formation apparatus; and then an undercoat layer and a magnetic layer are formed on the substrate.
However, in the case of the aforementioned conventional magnetic recording medium including a non-magnetic metallic substrate such as an aluminum substrate or a non-metallic substrate such as a glass substrate, when a hard film formed from NiP, which is provided on the substrate, is subjected to texturing, the magnetic anisotropy of a magnetic layer can be enhanced but the surface smoothness of the medium tends to be lowered because of surface irregularities of the hard film. Consequently, glide height characteristics are deteriorated, and attainment of high recording density becomes difficult. In addition, the production process for the magnetic recording medium includes complicated production steps, resulting in high production costs.
In view of the foregoing, an object of the present invention is to provide a magnetic recording medium which exhibits excellent magnetic characteristics such as thermal stability and excellent glide height characteristics and which is easily produced.
Another object of the present invention is to provide a process and apparatus for producing the magnetic recording medium easily.
A further object of the present invention is to provide a magnetic recording and reproducing apparatus incorporating the magnetic recording medium exhibiting excellent magnetic characteristics such as thermal stability.
The present inventors have found that the thermal stability of a magnetic recording medium can be considerably enhanced when an orientation-determining layer is formed between a non-magnetic substrate and a non-magnetic undercoat layer, the orientation-determining layer has a crystal structure in which columnar fine crystal grains are inclined at an angle in a radial direction, the ratio of a coercive force in a circumferential direction of a magnetic layer (Hcc) to a coercive force in a radial direction of the magnetic layer (Hcr); i.e., Hcc/Hcr, is more than 1, and the magnetic layer includes a plurality of magnetic films and has a structure such that antiferromagnetic bonding can be formed between the magnetic films. The present invention has been accomplished on the basis of this finding.
Accordingly, the present invention provides a magnetic recording medium comprising a non-magnetic substrate, an orientation-determining layer for causing the non-magnetic undercoat layer to have a predominant plane of (200), a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in order, wherein the non-magnetic undercoat layer has a bcc structure; the orientation-determining layer has a crystal structure in which columnar fine crystal grains are inclined in a radial direction; the ratio of a coercive force in a circumferential direction of the magnetic layer (Hcc) to a coercive force in a radial direction of the magnetic layer (Hcr); i.e., Hcc/Hcr, is more than 1; and the magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110) plane, and permits antiferromagnetic bonding to be formed therebetween.
In the magnetic recording medium of the present invention, since the orientation-determining layer having a crystal structure in which columnar fine crystal grains are inclined in a radial direction is provided, the ratio of a coercive force in a circumferential direction of the magnetic layer (Hcc) to a coercive force in a radial direction of the magnetic layer (Hcr); i.e., Hcc/Hcr, is more than 1. Thus the magnetic anisotropy of the magnetic layer in a circumferential direction can be enhanced and crystal magnetic anisotropy constant (Ku) can be enhanced. Consequently, magnetic characteristics, such as thermal stability, coercive force, and S/N ratio of recorded/reproduced signals, can be enhanced.
In addition, in the present invention, due to antiferromagnetic bonding between magnetic films, magnetic films other than a primary magnetic film of largest coercive force assume an apparent non-magnetized state; or the primary magnetic film assumes a state in which apparent magnetization of the primary magnetic film is reduced in an amount corresponding to the magnetization of magnetic films other than the primary magnetic film.
Therefore, the volume of magnetic grains can be increased sufficiently without adversely affecting noise and resolution, and thermal stabilization can be attained; i.e., thermal stability can be enhanced.
The magnetic layer may have a laminated ferrimagnetic structure in which the directions of the magnetic moments (or the directions of the magnetization) of adjacent magnetic films are opposite to each other.
The magnetic layer may have a structure including a plurality of magnetic films and an intermediate film provided therebetween.
The magnetic layer may have two or more laminated structures, each including a magnetic film and an intermediate film adjacent thereto.
Preferably, the antiferromagnetic bonding magnetic field of a magnetic film adjacent to a primary magnetic film having the largest coercive force among a plurality of magnetic films is larger than the coercive force of the magnetic film adjacent to the primary magnetic film.
Preferably, the intermediate film is formed from a material predominantly comprising at least one element selected from among Ru, Cr, Ir, Rh, Mo, Cu, Co, Re, and V.
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200); i.e., a composition formed of one or more elements selected from among Cr, V, Nb, Mo, W, and Ta.
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200); i.e., a composition formed of an alloy predominantly containing Cr.
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200); i.e., a composition predominantly containing a Ta-containing alloy X1Ta (wherein X1 is one or more elements selected from among Be, Co, Cr, Fe, Nb, Ni, V, Zn, and Zr), and may have an Fd3m (space group notation) structure or an amorphous structure.
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200); i.e., a composition predominantly containing an Nb-containing alloy X2Nb (wherein X2 is one or more elements selected from among Be, Co, Cr, Fe, Ni, Ta, V, Zn, and Zr), and may have an Fd3m structure or an amorphous structure.
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200); i.e., a composition predominantly containing CoTa (Ta content: 30-75 at %) or CoNb (Nb content: 30-75 at %), and may have an Fd3m structure or an amorphous structure.
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200); i.e., a composition predominantly containing CrTa (Ta content: 15-75 at %) or CrNb (Nb content: 15-75 at %).
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200); i.e., a composition predominantly containing NiTa (Ta content: 30-75 at %) or NiNb (Nb content: 30-75 at %), and may have an Fd3m structure or an amorphous structure.
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200) plane; i.e., a composition containing a non-magnetic metal having an Fd3m structure.
The orientation-determining layer may have a composition which causes the non-magnetic undercoat layer having a bcc structure to have a predominant orientation plane of (200); i.e., a composition containing a non-magnetic metal having a C15 structure.
In the present invention, an orientation-enhancing layer may be formed between the non-magnetic substrate and the orientation-determining layer.
The orientation-enhancing layer may comprise a material having a B2 structure or an amorphous structure.
The orientation-enhancing layer may predominantly comprise any one selected from among NiAl, FeAl, CoAl, CoZr, CoCrZr, and CoCrC.
In the present invention, a plurality of orientation-determining layers may be provided.
The present invention also provides a magnetic recording medium comprising a non-magnetic substrate, an orientation-determining layer for arranging the crystal orientation of a layer provided directly thereon, a magnetic layer, and a protective layer, the layers being formed on the substrate, wherein the orientation-determining layer has a crystal structure in which columnar fine crystal grains are inclined in a radial direction; the ratio of a coercive force in a circumferential direction of the magnetic layer (Hcc) to a coercive force in a radial direction of the magnetic layer (Hcr); i.e., Hcc/Hcr, is more than 1; and the magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and permits antiferromagnetic bonding to be formed therebetween.
The present invention also provides a magnetic recording medium comprising a non-magnetic substrate, an orientation-determining layer for arranging the crystal orientation of a layer provided directly thereon, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in order, wherein the non-magnetic undercoat layer has a bcc structure; the orientation-determining layer is formed from an NiP alloy having an amorphous structure, and can cause the non-magnetic undercoat layer to have a predominant orientation plane of (200); the ratio of a coercive force in a circumferential direction of the magnetic layer (Hcc) to a coercive force in a radial direction of the magnetic layer (Hcr); i.e., Hcc/Hcr, is more than 1; and the magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and permits antiferromagnetic bonding to be formed therebetween.
The orientation-determining layer may comprise nitrogen or oxygen in an amount of at least 1 at %.
The present invention also provides a process for producing a magnetic recording medium comprising a non-magnetic substrate, an orientation-determining layer for causing the non-magnetic undercoat layer to have a predominant orientation plane of (200), a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in order, wherein the non-magnetic undercoat layer has a bcc structure; and the magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and permits antiferromagnetic bonding to be formed therebetween, which process comprises forming the orientation-determining layer by releasing film formation particles containing a material constituting the layer from a release source, and then depositing the particles onto a deposition surface, wherein the direction of the trajectory of the film formation particles is controlled so that a projection line of the trajectory of the particles formed on the deposition surface lies substantially along a radial direction of a non-magnetic substrate, and the incident angle of the trajectory of the particles is 10-75xc2x0 with respect to the non-magnetic substrate.
The orientation-determining layer may be subjected to oxidation or nitridation.
The orientation-determining layer may be formed through sputtering using a sputtering target serving as a release source of film formation particles.
When the orientation-determining layer is formed, the layer may be subjected to oxidation or nitridation using a sputtering gas containing oxygen or nitrogen.
The oxidation or nitridation may be carried out by bringing the surface of the orientation-determining layer into contact with an oxygen-containing gas or a nitrogen-containing gas.
The present invention also provides an apparatus for producing a magnetic recording medium comprising a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in order, wherein the non-magnetic undercoat layer has a bcc structure; an orientation-determining layer for causing the non-magnetic undercoat layer to have a predominant orientation plane of (200) is formed between the non-magnetic substrate and the non-magnetic undercoat layer; and the magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and permits antiferromagnetic bonding to be formed therebetween, which apparatus comprises a release source for releasing film formation particles containing a material constituting the orientation-determining layer, the layer being formed through deposition of the particles onto a deposition surface; and means for controlling the direction of the trajectory of the film formation particles released from the release source. The direction-controlling means can control the direction of the trajectory of the particles so that a projection line of the trajectory of the particles formed on the deposition surface lies substantially along a radial direction of a non-magnetic substrate, and the incident angle of the trajectory of the particles is 10-75xc2x0 with respect to the non-magnetic substrate.
The present invention also provides a magnetic recording and reproducing apparatus comprising a magnetic recording medium, and a magnetic head for recording data onto the medium and reproducing the data therefrom, wherein the magnetic recording medium comprises a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in order, wherein the non-magnetic undercoat layer has a bcc structure; an orientation-determining layer for causing the non-magnetic undercoat layer to have a predominant orientation plane of (200) is formed between the non-magnetic substrate and the non-magnetic undercoat layer; the orientation-determining layer has a crystal structure in which columnar fine crystal grains are inclined in a radial direction; the ratio of a coercive force in a circumferential direction of the magnetic layer (Hcc) to a coercive force in a radial direction of the magnetic layer (Hcr); i.e., Hcc/Hcr, is more than 1; and the magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and permits antiferromagnetic bonding to be formed therebetween.